1. Field of the Invention
The present invention relates to an addition reaction-curable pressure-sensitive adhesive composition which forms a cured product layer that can be peeled from a release film with minimal peeling force and exhibits excellent adhesion even to silicone rubbers. The invention also relates to a pressure-sensitive adhesive tape that uses the composition.
2. Description of the Prior Art
Pressure-sensitive adhesive tapes and pressure-sensitive adhesive labels that use a silicone pressure-sensitive adhesive comprise a silicone pressure-sensitive adhesive layer that exhibits excellent levels of heat resistance, cold resistance, weather resistance, electrical insulation and chemical resistance, and they are therefore used under severe conditions, such as very high or very low temperatures, where organic resin-based pressure-sensitive adhesives such as acrylic pressure-sensitive adhesives or rubber-based pressure-sensitive adhesives would suffer deformation or degradation.
Further, silicone pressure-sensitive adhesives exhibit excellent adhesion to all manner of adherends. Silicone pressure-sensitive adhesives also exhibit adhesion to a variety of surfaces that are difficult to bond using organic resin-based pressure-sensitive adhesives such as acrylic pressure-sensitive adhesives or rubber-based pressure-sensitive adhesives, the surfaces including silicone rubbers, silicone release papers, surfaces that have been coated with a release agent, water repellent agent, antifouling agent, paint or coating agent or the like that contains silicone, fluororesins, and surfaces that include a fluororesin component. Accordingly, silicone pressure-sensitive adhesives are ideal for use within pressure-sensitive adhesive tapes used when bonding or fixing a silicone rubber member to another member. However, in recent years there have been growing demands for pressure-sensitive adhesives that are capable of bonding together members of greater mass and capable of producing a bonded interface that is able to withstand greater impact than that achievable using conventional pressure-sensitive adhesives, and therefore there is a need to further improve the adhesive strength of silicone pressure-sensitive adhesives to silicone rubbers.
To provide a specific example, a silicone pressure-sensitive adhesive is used in the pressure-sensitive adhesive tape used for bonding the key tops to a silicone rubber key pad, and in order to ensure superior durability to repeated keystrokes, the pressure-sensitive adhesive tape must be resistant to peeling under all manner of environments from low temperature to high temperature.
When a pressure-sensitive adhesive tape that uses a conventional silicone pressure-sensitive adhesive is employed for the type of application described above, if the shape of the member being bonded is such that a satisfactory bonding surface area cannot be ensured, then detachment of the member may occur as a result of peeling of the pressure-sensitive adhesive tape.
On the other hand, silicone pressure-sensitive adhesive compositions comprising an organosilicon compound having B—O—Si bonds are already known (see Patent Document 1). However, although Patent Document 1 states that these compositions provide improved adhesive strength to silicone rubbers, these compositions still suffer from inadequate adhesive strength to silicone rubbers, and the compositions may also suffer from reduced adhesive strength to adherends other than silicone rubbers.
Further, silicone pressure-sensitive adhesive compositions that use a mixture of a diorganopolysiloxane containing alkenyl groups and a polyorganosiloxane containing no alkenyl groups are also known (see Patent Document 2), and Patent Document 2 states that these compositions provide improved adhesive strength to silicone rubbers, but the adhesive strength of these compositions to silicone rubbers also still tends to be inadequate.
In some cases, a release film may be bonded to the silicone pressure-sensitive adhesive surface of a pressure-sensitive adhesive tape prior to use of the tape in order to protect the silicone pressure-sensitive adhesive surface. A release film coated with a silicone-based release agent containing a fluorine-containing substituent is typically used for protecting the silicone pressure-sensitive adhesive surface. This release film is peeled away and removed from the silicone pressure-sensitive adhesive surface when the pressure-sensitive adhesive tape is used, and therefore it is desirable that the release film is able to be peeled off with minimal force. In the case of a pressure-sensitive adhesive tape that uses an aforementioned silicone pressure-sensitive adhesive composition comprising an organosilicon compound having B—O—Si bonds (Patent Document 1), peeling of the release film tends to require considerable force.    [Patent Document 1] JP 7-11228 A    [Patent Document 2] JP 2008-24777 A